I like the idea of have Google assistant, Alexa and Sense companion on one phone. They all have their strengths and weaknesses. Google is not the best for shopping compared to Alexa. Google doesn't have as many partners as Alexa for smart Tech to use at home and Alexa has well of 3000 skills.
Google works better with stuff on your phone and has an amazing search engine.
But if you don't want to use Alexa or Google assistant that's up to you but it's great to have choice.
As for Sense Companion, it's not a voice assistant. But I like how it can tell you to charge you phone because it worked out you don't have enough battery to last for the event your going out to in the evening.
Just stick with Google Assistant on your phones, manufacturers. We don't need more assistants, Google Assistant is perfectly fine.
Well, basically we can say that it is unneeded, to have two virtual personal assistants and considering that the Google Assistant already performs almost (or all) the same commands and that is even better because it is more polished, consistent, etc. So basically that's pretty all. But on the other hand, to try to understand so why most probably HTC did it. Probably for two main reasons. 1, because very probable it has some financial reasons with Amazon. And 2, to maybe give the impression that not only Samsung, etc., (offers) has 2 virtual assistants (Google & Bixby). Although even regarding that, there is so much to say.